1. Field of the Invention
The present invention relates to torque converters, and more particularly to a torque converter having a fluid damping function.
2. Description of the Related Art
DE 44 24 704 C2 discloses a torque converter in which a clutch piston is connected to a turbine impeller hub via a torsional vibration damper. In this case, a hub part of the torsional vibration damper is fixedly coupled to the turbine impeller hub, and two back-shroud parts extending on either side of the hub part are fixedly fitted onto the clutch piston. In the radially outer region, the two back-shroud parts form an annular space which extends around the axis of rotation of the converter and has an approximately square cross section. Arranged in this annular space are individual casing segments, which respectively form a virtually fluidtight inner space, which is open through an opening to the radially inner end. A projection protruding radially outward on the hub part engages in this opening. Coupled to this projection in the inner space is a displacement element, which is at a predetermined distance from the walls bounding the inner space. If torsional vibrations which lead to a relative torsion between the hub part and the two back-shroud parts occur, the hub part engaging in the inner space shifts, with the displacement element mounted on it, in the inner space. The fluid present in the inner space is thereby displaced resulting in a nozzling effect being produced between the displacement element and the walls bounding the inner space. Consequently, vibrational energy can be dissipated by the fluid which is arranged in the inner space and flows through between the wall and the displacement element.
In the case of this known torque converter, the fluid vibration damping arrangement leads to vibration damping proportional to the rate of relative torsion. However, the provision of the fully enclosed inner space with the displacement element movable therein leads to a complex construction with a correspondingly large axial extent.
U.S. Pat. No. 5,655,368 discloses a torque converter in which a plurality of displacement blades extending radially outward are provided on the turbine impeller shell. A plurality of corresponding projections, extending radially inward, are found on the casing. If rotational vibrations occur in the engaged state of the lockup clutch., the blades or projections shift in relation to one another, causing the fluid contained in the interior of the converter to be displaced, which leads to fluid vibration damping. However, there is a problem with this known torque converter in that the fluid damping effect also occurs in the disengaged state of the lockup clutch. The result is that the expected motion of the turbine impeller in the converter is disadvantageously affected.